ABSTRACT Thegenomeprovidesaprecise,biologicalblueprintoflife.Toimplementthisblueprintcorrectly,thegenome mustbereadwithgreatprecision;?however,duetotheconstraintsofbiologicalfidelity,itisimpossibleforthis process to be completely error-free. As a result, transcription errors can occur at any time, in any transcript, andhowtheserandomerrorsaffectcellularhealthiscompletelyunknown.Tofillthisgapinourknowledge,we recently monitored yeast cells that were genetically engineered to display error-prone transcription. We discovered that transcription errors give rise to misfolded proteins that induce proteotoxic stress. Ultimately, this stress can overload the protein quality control machinery and allow proteins associated with Alzheimer?s disease, amyotrophic lateral sclerosis, Huntington?s disease or prion disease to escape degradation, which promotes their aggregation and enhances their toxicity. Thus, transcription errors represent a new molecular mechanism by which cells can acquire disease. As a result, it will be important to learn more about the mechanisms that induce or suppress transcription errors, because these mechanisms could either delay or accelerate the progression of proteotoxic diseases. To this end, we recently developed the first next-gen sequencingassaythatiscapableofmeasuringthefidelityoftranscriptioninagenome-widefashion.Wenow propose to use this technology on yeast and mice to identify the parameters that control the fidelity of transcription in eukaryotic cells. These experiments will exploit the genetic flexibility of yeast to dissect how specific alleles, genes and pathways affect the fidelity of transcription, and make use of the biological complexityofmicetodeterminehowaging,tissuespecificityandcelltypesinfluencethetranscriptionalerror rate.Together,theseexperimentswillprovidethefirstcomprehensive,genomewideanalysisoftranscriptional fidelity in eukaryotic cells. In addition, we propose to use newly developed mouse models of transcriptional mutagenesis, as well as precise experiments in yeast, to discover how transcription errors affect the aging processasawhole,andAlzheimer?sdiseaseinparticular.Theseexperimentscouldrevealnovel,mechanistic links between some of the most important forces in human aging and help explain why normal aging contributestodisease.